The objective of this research is to determine if exposure to ultrasound can enhance the effects of x-irradiation on tumors. There is considerable evidence in the literature on the enhancement by hyperthermia of the effects of ionizing radiations on tumors. One of the effects of ultrasound is heating; this effect is responsible for some but not all of its biologic effects. It is our intention to study the effect of application of varying levels and durations of ultrasound before, during, and after tumor irradiation. Ultrasonic enhancement of the irradiation will be measured as a reduction in the radiation dose required to cure 50 percent of the tumors, the TCD50. The combination of ultrasound and fractionated radiotherapy as well as possible differences in effect when the ultrasound is pulsed rather than as continuous wave will also be studied.